Thermographic copying

ABSTRACT

A process for the reproduction of a transparent original having infrared radiation and visible light absorptive image markings thereon by exposing the original to infrared radiation and/or light while the image markings are arranged in heat-conductive contact with a recording layer composed at least 80 percent by weight of gelatin and having distributed therethrough a finely divided substance transforming absorbed visible and infrared radiation into heat, for a period not longer than 10 1 second and developing the recording layer by washing with water to remove the gelatin in the area corresponding with the non-image area of the original.

United States Patent [19'] Vrancken 1111 3,811,773 [451 May 21, 1974 1THERMOGRAPHIC COPYING Marcel Nicolas Vrancken, Parklaan, Belgium [73]Assignee: Agfa-Gevaert N.V., Mortsel,

Belgium [22] Filed: June 1, 1971 [21] Appl. No.: 149,039

Related US. Application Data [75] Inventor:

[63] Continu'ation-in-part of Serv No. 560,314, June 24,

1966, abandoned.

[30] Foreign Application Priority Data Nov. 26, 1965 Great Britain50441/65 [52] US. Cl 355/132, 96/35, 250/317, 355/32, 355/78, 355/88[51] Int, Cl. G03b 27/02 [58] Field of Search 96/27 R, 35, 36.3;260/317, 316; 355/132 [56] ReferencesCited- UNITED STATES PATENTS,

3,523,791 8/1970 Vranck-en et al. 96/35 X Gosnell 250/316 X 3,476,57811/1969 Bl'inckmannn. 250/317 X 3,514,597 5/1970 Haes et a1. 250/317 X3,121,162 2/1964 Roman et a1. 117/17 X 3,298,833 l/l967 Gaynor 96/27Primary Examiner-Richard L. Moses Attorney, Agent, or Firm-William J.Daniel [5 7] ABSTRACT A process .for the reproduction of a transparentoriginal having infrared radiation and visible light absorptive imagemarkings thereon by exposing the original to infrared radiation and/orlight while the image markings are arranged in heat-conductive contactwith a recording layer composed at least 80 percent by weight of gelatinand havingdistributed therethrough a finely divided substancetransforming absorbed visible and infrared radiation into heat, for aperiod not longer than 10 second and developing the recording layer bywashing with waterto remove the gelatin in the area corresponding withthe non-image area of the original.

12 Claims, 1 Drawing Figure PATENTEDIAYZI mm 381L773 INVENTOR I 5% Md/Qww ATTORNEY THERMUGRAPHHC corriur;

The present invention is a continuation-in-part application of the US.Patent application Ser. No. 560,314 now abandoned filed with the US.Patent Office on June 24, 1966.

The present invention relates to a method for recording'and reproducinginformation by means of electromagnetic radiation which by absorption ina thermosensitive layer produces an increase in temperature therein.

From the US. Pat. No. 3,121,162 by P. A. Roman and U. E. lfaff, issuedFeb. 11, 1964 a reproduction process is known comprising irradiating asubject having heat absorptive image areas with infrared radiation inheat-conductive contact with a supported layer of high jelly strengthgelatin, sufficiently to raise the temperature of the gelatinsubstantially in regions of. said heat absorptive image areas so .that asubstantial increase in swelling tendency of the gelatin in said areasis caused, moistening the gelatin layer and pressing it into contactwith an absorbent support to cause the gelatin in said areas to adhereto said support, and separating the gelatin layer from said support toleave a stratum of the gelatin of said areas on the support.

According to one contact-printing embodiment described in said patentspecification a documenthaving a transparent or slightly diffusingsupport is copied by placing the printed characters of the document inheat conductive contact with the gelatin layer which may contain apigment that does not absorb infra-red radiation and exposing thegelatin layer to infra-red radiation through the support of thedocument. A laterally reversed master sheet is thus obtained andaccordingly, right-reading positive copies are obtained by transfer. Inthis case only one-sided documents can be copied.

According to another contact-printing embodiment described in said US.Pat. specification an original comprising a heat-diffusing support isplaced with that support in contact with the gelatin layer which maycontain colouring materials, carbon black, etc., and exposure is madethrough the document towards the gelatin layer. The copy obtained on areceivingsheet by transfer is laterally reversed and the image-sharpnessis not of high quality.

According to the present invention, a process for recording informationis provided wherein is used a recording material comprising a gelatinlayer containing a uniformly distributed visible and infra-red lightabsorbing substance which as a result of such absorption becomes heated;and this gelatin layer is exposed, through a copying light transmittingoriginal disposed with its image-markings in direct thermal contact withthe gelatin layer of said recording material, said image markings beinglight-absorbing and heatable by copying lightin the wavelength range ofvisible and infra-red light, the exposure being of a'duration not longerthan second and of such intensity that a substantial increase in theswelling tendency of the gelatin in said recording layer is producedselectively in correspondence with the non-image parts of said originalbut insufficient to produce a substantial increase in the swellimagearea.

' It will be apparent that by this process a laterally reversed recordof the original text or other matter constituted by said light-absorbingimage portions, is ob tained. If the support of the recording layer istransparent, the copy will belegible through its backing. De-

pending on the composition of the recording material, this record may berendered visible in or on the said recording material and/or may be usedfor forming one or more non laterally reversed copies on anothermaterial.

It is stressed that the 'lightabsorbing image portions of the originaland the gelatin recording layer are in heat-conductive contact duringthe exposure, hereby the distance between the copying material and therecording medium is as small as possible. This is an important featurein the production of very sharp copies.

An important discovery leading to the invention is that by asufficiently brief exposure to light (an exposure time not higher than10 sec.) the existence of a heat-conductive relationship between thelightabsorbing image portions and the gelatinrecording layer is of noeffect or substantially no effect in forming the record in the gelatinrecording layer. On the contrary, the record is produced by virtue ofthe internal heating of the gelatin recording layer where it isirradiated with light passing through the non-image areas of theoriginal. Consequently there is no need to insulate the light-absorbingimage portions from the gelatin recording layer; they can be maintainedin intimate contact during the exposure, by pressing the original andthe recording material together. If the materials are merely laid nextto each other and the image-bearing face of the original or the gelatinrecording layer are i not coated in any way, then there may be present avery thin air interlayer which would however not prevent effective heatconduction of the lighbabsorbing image performed using for the exposurea gas discharge lamp V having an exposure time of no longer than 10seconds.

According to a preferred embodiment the exposure is carried out by meansof electromagnetic radiation the greater part of which (at least percentof the ir-. radiation energy) is composed of electromagnetic radiationof the visible spectrum. By a short duration exposure of sufficientintensity (at least 0.2 watt sec per'sq. cm and preferably 0.50 to 1.0watt. sec per sq. cm) sufficient heat can be produced in thelight-in-heatconverting particles distributed throughout the gelatinlayer which are irradiated, for suddenly increasing the temperature ofthe gelatin surrounding such particles 1 and conferring on suchsurrounding gelatin a substantial increase in swelling tendency in waterand solubility in 'water or an aqueous composition. On the other hand,the dosage of short duration high intensity exposing light is such'thatnot enough heat can be absorbed in he light-absorbing image portions ofthe original for being transferred to the gelatin recording layer tobring about any significant differentiation in water solubility.

According to our invention due to the intimate contact of the imageportions of the original with the heat-sensitive gelatin layer at themoment of exposure legible images of extremely high resolution andsharpness can be obtained by washing-off the internally heated gelatinportions of the recording layer.

The copying light-absorbing substance in the gelatin layer may bedispersed or dissolved in the gelatin layer. One or more than one suchsubstance may be present in one and the same layer.

It is preferred to use in the heat-sensitive gelatin layer a copyinglightabsorbing substance in such a proportion that the absorptiontherein of light energy produced on flash exposure effects a sufficientincrease in temperature of the gelatin to increase its water solubilityto such an extent that it can be dissolved in the heated areas bycoldwater (2025"C).

In order to achieve as high a conversion of light into heat as possibleinthe substance(s) dispersed or dissolved in the gelatin, it ispreferable that such substance(s) neither take'part in an endothermicchemical reaction during exposure nor undergo a change in aggregationstate.

In order to obtain an economic use of the light energy penetrating intothe gelatin layer, the light absorbing substance is preferably presenttherein in such an amount that at least 80 percent of such light isabsorbed and converted into heat. in general it is recommended that theoptical density of the gelatin layer be comprised between 1 and 3, thegelatin content of such layer being in that case between 1 and 4' g persquare metre. Thus the gelatin recording layer may containlight-absorbing substance to an optical density of at least 1. I

In preparing a heat-sensitive material for use in the .process of thepresent invention the gelatin recording layer may be applied to atransparent support but this is not essential. An opaque or translucentsupport may be used. By way of example the said recording layer may beapplied to atransparent film, a paper support or a metal support. Theselected support iscoated with a composition preferably containing atleast 80 percent by weight of gelatin. That gelatin composition containsone or more dissolved or finely dispersed visible light absorbing orvisible light and infra-red absorbing substances which transform suchlight into heat. Certain preferred substances which absorb visible lightand infra-red light and convert the absorbed radiation into heat arefinely divided carbon black, graphite, prussian blue, oxides, sulphidesor carbonates of heavy metals, particularly of those heavy metals havingan atomic weight between 45 and 210, such as manganese or lead sulphideor such heavy metals themselves in finely divided state, e.g., silver,bismuth, lead, iron, cobalt and nickel. Carbon particles and silver areamong the most suitable substances.

For further examples and data relating to pigments form part of thepresent disclosure and should be read in conjunction herewith.

It is preferred to employ dispersed light absorbing particles,preferably having a particle size or an average particle size notgreater than 0.1 u.

The gelatin of the heat-sensitive layer may be of the type of gelatinnormally used in silver halide photography.

A sufficient Bloom gel strength (preferably at least 150) of the gelatinis important in cases wherein the gelatin has to be swollen andtransferred in swollen state to a receiving support, e.g. a screeningmaster blank such as a Japan paper, however, in the case that theoriginal is to be reproduced merely by exposure and washing away of theheated areas a high bloom gel strength of the gelatin is not necessary.Suitable gelatin for application in the present invention is describedeg in UK. Patent Specification 1,154,902. 7

The differential swelling tendency of the gelatin layer can be observeddirectly when moistening the layer with water. The swelling tendency andsolubility of the gelatin varies with the hardening degree. After asudden heating above C a substantially unhardened gelatin layer willhave regions which can be washed away completely by water at 25C.

According to a special embodiment the gelatin layer contains during theexposure uniformly distributed coloured substances which absorb light ofa determined part of the visible spectrum and convert it into heat. Agelatin layer made spectrally sensitive in this way can be used forrecording coloured originals in terms of differences in solubility andin swelling tendency in water.

it will be understood that mixtures of said coloured substances can alsobe used, so that light of the entire visible spectrum is absorbed.Furthermore, the substances need not absorb exclusively in the range ofthe visible spectrum; they may also absorb in the infrared region.

The coloured substances or mixtures of said substances preferably absorblight corresponding to at least one of the primary colours (red, green,blue) or subtractive colours (cyan, magenta, yellow).

Substances that absorb visible light of a part of the visible spectrumand wherein absorbed light energy is converted into heat are e.g. dyesbelonging to the which absorb visible light and convert it into heat,reference is particularly made to Belgian Patent Specification 7,502 andthe UK. Patent Specification 1,160,221 corresponding with the US. Pat.application Ser. No. 550,834, which specifications are deemed to classesof the azo dyes, the triarylmethane dyes, the xanthene dyes, theacridine dyes, the methine dyes, the azine dyes, the phthalocyaninedyes, the anthraquinone dyes and allied dyes.

Said substances can be used in dispersed or dissolved condition; whenthey are used in dispersed form they should preferably have a grain sizelowe than 0.1 1.4..

According to the present invention, when using spectrally sensitivegelatin layers, it is possible to produce printing masters suitable forcolour printing and for producing multicolour copies of colouroriginals. For that purpose three materials are used that contain aheat-sensitive gelatin layer comprising a substance which is heated onabsorbing red, green and blue light respectively, i.e. a gelatin layercontaining a cyan dye,

a magenta dye and a yellow dye respectively. Said dyes may be dyessuitable for hectographic printing.

By the heat produced in the heat-sensitive gelatin layer containing thecyan dye said layer is made more swellable and water-dissolvable in theareas corre- By the heat produced in the heat-sensitive gelatin I layercontaining the magenta dye said layer is made more swellable andwater-dissolvable in the areas corresponding to the green areas of theoriginal to which it was exposed.

By the heat produced in the heat-sensitive gelatin layer containing theyellow dye said layer is made more swellable and water-dissolvable inthe areas corresponding to the blue areas of the original to which itwas exposed.

Multicolour prints can be produced by using the three exposed materialsto prepare three separate masters which are used to print in register.

For reproducing originals that contain separate markings in the pureprimary colours, blue, green and red (e.g. a transparency containingblue, green and red letters), three separate gelatin layers can be usedwhich are sensitized'for blue, green and red respectively by a blue,green and red dye or pigment that is uniformly distributed therein. Bywashing away the selectively heated gelatin portions copies of the imagemarkings in the primary colours are obtained that canbe inspected inoverlay.

The effectiveness of the recording substantially depends on theintensity of the radiant energy. For example, a gelatin recording layer,that does not provide a I sufficient differentiation in swellingtendency with a particular source of electromagnetic radiation energymay be fully effective if the energy level is substantially increased. r

Lamp structures and exposure systems producing electromagnetic radiationat least 70 percent of which consists of visible light (in other wordscontaining only small amounts of U.V. light and infra-red light) andwhich are capable of providing high intensity radiation in a very smalllapse are preferably used.

Radiation sources emitting visible light of high intensity in a verysmall lapse of time are so-called flash lamps and more particularly thedischarge lamps containing a noble gas.

in the present invention good results are obtained with a Xenon gasdischarge lamp, which can supply an energy of 300l,000 watt. sec in atime interval of to 10" seconds and can irradiate the recording layerwith an energy of at least 0.2 watt. sec per sq. cm and preferably inthe range of 0.2 to 1.5 watt. sec per sq.

According to a preferred embodimentof the invention a gas discharge lampis used, which is in the form of a thin tube fitted in a hollow glasscylinder in order to makepossible a uniform exposure of the recordingmaterial applied according to the periphery of the cylinder.

More details about copying apparatus containing such a discharge lampcan be found in Belgian Patent Specification 664,868. The intensity ofthe emitted light is particularly high in the regions of the visiblespectrum. v y

it is possible to employ a number of flash tubes operatingsimultaneously, or to obtain a suitable imagedifferentiation by flashinga single tube at suitable intervals. Reflectors and other opticalcomponents may be included to provide irradiation of maximum uniformity.

Evidently lamps with a lower energy output can be used if the emittedlight energy is focused onto a relatively small heat-sensitive area. So,e.g., a gas discharge lamp with an energy output of 40 watt. sec. issuited for copying 6 cm X 6 cm and 6 cm X 9 cm originals on aheat-sensitive material as described in the present invention. It isfurther self-explanatory that exposure may be progressive andintermittent. In other words the heat-sensitive material may be scannedthrough an original with a light-spot of high intensity, e.g. a laserbeam, or may be progressively exposed through a slit wherein, e.g.,copying light of a continuously emitting tube-like radiation source isfocused.

As a particular example of the use of the invention it may be used forproducing positive-positive prints of an original provided in the formof a silver image transpar- The. following examples illustrate thepresent invention without limiting it thereto. Example 1 i Apoly(ethylene terephthalate) support of 0.1 mm thickness provided with asubbing layer for gelatin is coated with the following composition prorata of 30 g/sq.m:

l0 aqueous solution of gelatin having a Bloom gel strength value of 240250 g 50 aqueous dispersion of carbon black, having a particle size of0.1 p. 50 g water 200 g 5 aqueous solution of sodium tetradecyl sulphate25 g.

The layer is dried at,20C.

One arrangement of the materials of the invention for effectivereflectographic exposure is shown in the accompany drawing. In thisdrawing, the copying material 1 consisting of a transparent support 5and the thermosensitive gelatin layer 6 is laid on a photographic silverimage containing transparency 2 having radiationabsorbing markings 3 andradiation transmitting parts 4, the thermosensitive gelatin layer 6being in contact with the image layer 7 of the silver imagetransparency.

The sandwich of copying material and original is then braced around aglass cylinder 9 with the support 8 of the transparency in contact withsaid cylinder having a diameter of 8 cm.

Along the axis of this cylinder a xenon glass discharge lamp 110 isplaced which at the discharge between the electrodes 11 produces aradiation energy of 600 watt.

rate and extremely sharp copy of the original is ob-.

tained. Example 2 A cellulose triacetatesupport of 0.12 mm thicknessprovided with a subbing layer for gelatin is coated with the followingcomposition pro rata of 50 g per sq.m

l0 aqueous solution of gelatin with Bloom gel strength l 300 g 10aqueous dispersion of colloidal silver (average particle size 0.] p.)230 g 10 aqueous saponine solution 15 g The layer is dried at 20C,exposed and treated as described in Example 1. A very sharp and accuratep ,o th sri is Q z a n Example 3 A poly(ethylene terepththalate) supportof 0.1 mm thickness provided with a subbing layer for gelatin is coatedwith the following composition pro rata of 50 g per sq.m:

l aqueous solution of gelatin having a Bloom gel strength of 240 430 g Aviolet pigment dispersion known as Permanent violett R.L. Colanyl Teig"(C.l. 51,300) 20 g A green pigment dispersion known as Pigment grun BPigmosol (C.l. 10,006) 20 g 10 aqueous saponin solution 15 g 3 aqueoussolution of the sodium salt of the condensation product of oleic acidand methyltaurine 15 g The layer is dried at 20C, exposed and treated asdescribed in Example 1. A very sharp and accurate copy of the originalis obtained.

Example 4 v A paper support weighing 120 g per sq.m., provided on bothsides with a polyethylene coating and a subbing layer for gelatin, iscoated with the following composition pro rata of 50g per sq. m.:

'10 aqueous solution of gelatin having a Bloom gel strength of 190 410 g50 aqueous dispersion of carbon black of particle size 0.1 p. 30 g water50 g 5 aqueous solution of sodium tetradecylsulphate 25 g a finelydivided substance transforming absorbed visible and infrared radiationinto heat, said substance being present in such an amount that at leastabout 80 percent of said radiation towhich said recording layer isexposed is absorbed and converted into heat, said exposure being of aduration not longer than 10 second and of such an intensity that asubstantial increase in the swelling tendency of the gelatin in saidrecording layer is produced selectively in correspondence with thenon-image parts of said original but insufficient to produce asubstantial increase in the swelling tendency of the gelatin in the areaof the recording layer corresponding to the image area of the original,and developing said layer by washing with water to remove the gelatin inthe area corresponding to said non-image area.

2. A method for recording information according to claim 1, wherein saidgelatin has 21 Bloom gel strength value above 200.

3. A-method for recording information according to claim 1, wherein saidfinely divided substance(s) is a (are) pigment(s).

4. A method for recording information according to claim 3, wherein saidpigment(s) is (are) finely divided carbon particles.

5. A method for recording information according to claim 1, wherein theexposing radiation light contains at least percent of visible light.

6. A method for recording information according to claim 1, wherein theexposure is carried out with a flash lamp, and the irradiation is of anintensity of at least 0.2 watt.sec per sq.cm.

7. A method for recording information according to claim 6, wherein theradiation source is a high-intensity discharge lamp containing a noblegas.

8. A method for recording information according to claim 1, wherein thegelatin layer is applied to a support which is transparent to visiblelight.

9. A method for recording information according to claim 1, wherein saidsubstance(s) absorb(s) light within a determined part of the visiblespectrum and transform(s) it into heat.

10. A method for recording information according to claim 1, whereinsaid substance(s) is (are) present in the recording layer in such anamount that at least percent of the copying light is absorbed.

' 1 l. A method for recording information according to claim 1, whereinthe transmission exposure occurs through a silver image transparency.

12. A method for recording information according to claim 1, wherein theexposure has a duration not longer than 10" seconds.

1. A reproduction process which comprises contact exposing a transparentoriginal, having infrared and visible radiation absorptive imagemarkings, to radiation in the visible to infrared region of the spectrumwhile said markings stand in direct face to face contact with arecording layer containing at least 80 percent by weight of a gelatinand having distributed therethrough a finely divided substancetransforming absorbed visible and infrared radiation into heat, saidsubstance being present in such an amount that at least about 80 percentof said radiation to which said recording layer is exposed is absorbedand converted into heat, said exposure being of a duration not longerthan 101 second and of such an intensity that a substantial increase inthe swelling tendency of the gelatin in said recording layer is producedselectively in correspondence with the non-image parts of said originalbut insufficient to produce a substantial increase in the swellingtendency of the gelatin in the area of the recording layer correspondingto the image area of the original, and developing said layer by washingwith water to remove the gelatin in the area corresponding to saidnon-image area.
 2. A method for recording information according to claim1, wherein said gelatin has a Bloom gel strength value above
 200. 3. Amethod for recording information according to claim 1, wherein saidfinely divided substance(s) is a (are) pigment(s).
 4. A method forrecording information according to claim 3, wherein said pigment(s) is(are) finely divided carbon particles.
 5. A method for recordinginformation according to claim 1, wherein the exposing radiation lightcontains at least 70 percent of visible light.
 6. A method for recordinginformation according to claim 1, wherein the exposure is carried outwith a flash lamp, and the irradiation is of an intensity of at least0.2 watt.sec per sq.cm.
 7. A method for recording information accordingto claim 6, wherein the radiation source is a high-intensity dischargelamp containing a noble gas.
 8. A method for recording informationaccording to claim 1, wherein the gelatin layer is applied to a supportwhich is transparent to visible light.
 9. A method for recordinginformation according to claim 1, wherein said substance(s) absorb(s)light within a determined part of the visible spectrum and transform(s)it into heat.
 10. A method for recording information according to claim1, wherein said substance(s) is (are) present in the recording layer insuch an amount that at least 80 percent of the copying light isabsorbed.
 11. A method for recording information according to claim 1,wherein the transmission exposure occurs through a silver imagetransparency.
 12. A method for recording information according to claim1, wherein the exposure has a duration not longer than 102 seconds.